Fix TypeScript types

[danmichaelo]

Updates the TypeScript types to match the implementation, which only has a default export, not direct export of the four static methods.

Wrapped the methods in declare class Scrypt {} and added export default Scrypt at the end.

Tested with TypeScript 5.6.2 and ESM.

Note: My editor did a little bit of extra whitespace changes, let me know if you prefer to have these reverted.

[nikelborm]

For easier review
https://app.semanticdiff.com/gh/chrisveness/scrypt-kdf/pull/19/changes#scrypt.d.ts?ignore_comments=false